Vibrato apparatus



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July 17, 1951 a.. HAMMOND ETAL 2,560,568

VIBRATO APPARATUS Filed 001;. 10, 1946 2 i 2 Sheebg-Sheet l fnl/enfans aa/"6W5 Hammond 2 ./o/m M Hal/zert- July 17, 1951 l.. HAMMOND ETAL VIBRATO APPARATUS 2 Sheets-Sheet 2 Filed Oct. l0, 1946 *K5/af #f mmh. a /HM .s n mm. ad Ma Patented `luly 17, 1 951 VIBRATO APPARATUS Laurens. Hammond, Chicago, and John M. Hanert,

Park Ridge, Ill., assignors to Hammond Instrument Company, Chicago, Ill., a corporation of Delaware Application October 10, 1946', Serial No. 702,380

2 Claims. l

Our invention relates generally toelectrical musical instruments and more particularly to im-V proved capacitative scanningapparatus, particularly for use in musical instruments producing the vibrato effect.

The vibrato eiTect can be added to music or other sounds, while in the form of electrical signals, by transmitting the electrical signals through an artificial line and scanning the artificial line at a vibrato frequency, as disclosed in the prior patent to John M. Hanert, No. 2,382,413.

The object of the present invention is to provide an improved capacitative scanner for use in such vibrato apparatus.

A further object is to provide an improved means for maintaining an electrical contact with a rotating shaft which will not produce transients in low voltage signals transmitted through the Contact.

A further object is to provide an improved capacitor type scanning mechanism which `ds compact, which will be reliable in operation, and which may be economically manufactured.

Other objects will appear from the following description, reference being had to the accompanying drawings in which:

Figure l is an end elevational view of the vibrato apparatus, a portion of the casing being broken away to show the internal construction;

Figure 2 is a transverse sectional View taken on the line 2-2 of Fig. l, the synchronous motor being shown in elevation;

Figure 3 is a side elevational view of the scanning rotor;

Figure 4 is a plan view of the scanning rotor;

Figure 5 is a sectional View taken on the line 5 5 of Fig. 2;

Figure 6 is a sectional view taken on the line 6-6 of Fig. 5;

Figure '7 is a plan view of the artificial line components and case therefor; and

Figure 8 is a Wiring diagramV of a portion of theA artical line.

The scanning apparatus comprises a shell I0 closed by a flanged plate l2A (Fig. 2)A secured to the shell I0 by screws I4. The scanning device is driven by a synchronous motor IS- having a driving pinion |8- in mesh with a gear 20 mounted for relatively free rotation on a shaft 22. speed of the synchronous motor I6, and the gear ratio between pinion I-8 and gear 20 are such that the gear is driven at a speed of slightly less than '7 R. P. S. or about 400 R. P. M. A pair of flanged hubs 24, 25 are staked to the shaft 2i.` and form an abutment forV springs 26- and 21,

The i the other ends of which engage the gear 2.0. The springs 26 and 2l thus form a frictional resilient driving connection. between gear 2 0 and shaft 22. The hubsV 24, 2,5v also maintain the gear 20 perpendicular to the shaft 22.

The shaft 22A is mounted ina pair of self-aligning composition bearings 28 and 2.9, the bearing 28 being suitably secured between a bushing 30.

and a bearing support plate 32, the latter beingl suitably riveted to the wall I2. A disc-shaped thrust bearing is located in the bushing. 30. The bearing 29- is similarly clamped between a cupshaped casing 34 and a plate 36. The bearings 28v and 2-9 are each provided with an external groove around which threads 38 and 39 are wound, these threads passing through suitable apertures in the wall l2 and casing 34. The threads are made of cotton or similar material and lead to an oil cup, preferably through small diameters tubes. The threads thus form capillary conduits for conveying the oil from the oil cup to the bearings-- A metal hub 40 is secured to the outboard end of the sha-ft 22 by one or two set screws 4l, and has an insulating rotor arm 42 suitably secured to it. A metal rotor arm- 44` which is ribbed to render it more rigid, is riveted to the insulating rotor arm 42 and has a plurality of rotor or pickup plates 45 secured thereto. areY notched to engage the bent end 43 of the rotor arm 44. The plates 45y are preferably assembled to the middle arm 44 by placingthe plates in a suitable fixture and soldering the parts together by heating them in a high frequency electromagnetic eld. The rotor is statically and dynamically balanced by a pair of counterweights 46 riveted to the insulating rotor plate 42.

As the rotor rotates, the plates 45 thereof successively pass between groups of stator capacitor plates 48, each group being secured to a mounting bracket 50 in a manner similar to that by which the rotor plates 45 are secured to the rotor arm 44. Each of the brackets 50 is secured to the front wall I2 of the housing by a screw 52, the bracket being insulated from the wall by suitable insulating washers 54. A soldering lug 56 is provided beneath the head of each screw 52 for convenience in connecting wires to the brackets 50. In the embodiment illustrated sixteen groups of stator plates 48v are provided, each group consisting of siX plates. It has been found that this arrangement provides sufficient capacitative coupling between the rotor plates 45 and the groups of stator plates 4B to make certain that signals appearing on the stator plates will be impressed The plates 45- on the rotor plates without excessive loss in signal strength. It will be understood that the groups of stator plates are respectively connected through suitable gang switches to predetermined junction points in the articial line, as is more fully disclosed in the above mentioned patent No. 2,382,413.

The arm lil has an offset portion til with a bushing @Il held therein, this bushing forming a support for a pin 62 which is pressed into it. The pin 62 is made of a relatively hard, nontarnishing platinum alloy, such as a 90% platinum and ruthenium alloy or a platinumiridium alloy, and need be no greater than .032" in diameter. It is located in the bushing 64 so as to be accurately coaxial with the shaft 22.

A pair o1` studs 68 rivet a hanged casing sheet l@ to the housing lll, the portion of the housing wall around an opening l2 therein being flanged over the sheet lil to hold it in place against the wall of the housing it. A housing cover 'lli fits over the hanged sheet lt and is secured thereto by a pair of screws l.

An insulating mounting strip i8 is secured to the posts E58. A resilient brush arm Sil and a bifurcated spring anchor 82 are secured to the mounting strip lil. The brush arm 3&3, which is preferably made of a silicon or a phosphor bronze, has a brush button 8d, made of a relatively soft carbon or graphite, secured thereto, as by copper plating the carbon and then soldering the copper-plated button to the brush arm. The brush arm 8@ is iexed initially so as to press the brush contact 84 lightly against the end of the pin $2, which is spherically rounded to lessen abrasion.

Each of a pair oi contactors 86 and 8l has a peripheral groove for receiving a wire harness 88, and is provided with an eccentric hole slightly larger than the diameter of the pin G2. |The contactors 35 and 8l are made of pure carbon or graphite. The contactors v.are maintained in contact with the pin S2 by a pair of springs @il and 9i, respectively (Fig. 5), having one end hooked into loops formed in the harnesses 8S andV having their other ends hooked into the bent arms of the spring anchor 32. The connections of the ends of the Springs with the anchor 32 as well as with the wire harnesses S8 are soldered so as to assure that the springs will make a good electrical connection between the contactors 86, 8l and the anchor 82. The anchor 82, as well as the brush arm is secured to the insulating mounting strip 'i8 by a screw 92 and a clamping plate Sri. The spring anchor 32 has a soldering lug 'formed integrally therewith for connection to the output conductor 96 which is surrounded by a shielding sheath 98 (Fig. l), the latter having a bushing lil@ soldered thereto, and the bushing being secured in the housing shell "lll by a screw H02.

Since the holes in the contactors Si) and 3l' are eccentric .and their harness and springs so arranged as to cause any wear which may take place to be on the side of the hole nearest the center of the contactor, it will be apparent that a great deal of wear may take place before they fail. The platinum alloy pin does not tarnish under normal conditions and since it is substantially harder than the carbon of the brush lll and contactors 86, Sl, substantially all of the wear will take place in the latter elements. Since the erosion products of graphite are naturally iinely divided particles of graphite or carbon, they are conductive, and an extremely good electrical contact is maintained at all times. t has been found that after a short period of use the platinum alloy pin has microscopic depressions or crevices therein lled with particles of relatively soit graphite and the graphite thus acts in part as a lubricant and polishing agent, thereby limiting the wear between the two surfaces and substantially entirely eliminating any wear on the platinum alloy pin. This is la desirable effect since if the platinum alloy pin were abraded to any substantial extent the resulting platinum black, which offers a substantial high resistance, might interrupt the Contact and result in the production of noise in the output of the apparatus. The tension applied by the spring arm 8E] and the springs Qt and 9i is very small, in the order of a few grams, so that erosion of the graphite will take place very slowly, and since these springs pull upwardly on the pin 62 they lessen the load on the bearings 28 and 29.

' Since the holes in the contactors 3% and 8l are initially circular and of substantially the same diameter as that of the pin t2,there is little chance that any particle of dust or lint may work itself between contacting surfaces of these parts, and even after many years` of use, when Sonie wear has taken place in the contactors, no trouble is experienced due to dust and lint having collected around the contactors because there are no forces acting upon such particles which tend to draw them between the points of electrical contact. The contact Sli is likewise free from the possibility of having its electrical contact with the end of the pin 62 disturbed by the ingress of dust or lint.

Because of the importance of maintaining an uninterrupted contact with the pin E52, the three contacting elements 8B, 85 and 3l are provided, even though one such contact would be sufficient for ordinary purposes. However, by having three contactors, the possibility of interruption of the connection to the pin @2 is so small as to be practically non-existent.

This type of sliding electrical connection is unique in the respect that despite the low contact pressures employed the contact resistance is extremely low and does not vary to a measurable extent. Thus when transmitting a signal of very low voltage through the contacts it has been found that over very long periods. of time the signal is faithfully transmitted without the introduction of any transients. The contact arrangement is thus admirably suited for use in the scanner, since the signal picked up by the rotor plates l5 solely by virtue of their capacitative coupling with the stator plates i8, is necessarily of low amplitude.

The elements of the artificial line, schematically represented in Fig. 8, are shown in Fig. 7 as mounted in a boX lili] which may be made 0f wood and which is provided with a pair of channels Illl, m2 which extend longitudinally of the box. An intermediate strip of wood lll@ separates the channels and has a metallic terminal strip |06 suitably secured thereto. The edges of the channels Il and 162 are provided with a plurality of vertical extending slots Hi8 which extend into the wall at an angle of approximately 30. Slots IIB, each in alignment with one of the slots |08 are formed in the center strip H14 and are adapted to receive mounting platesy l I2 of Micarta or the like. A plurality of coils H6 (inductances LI to LM) are mounted one on each side of each of the mounting plates H2 with their axes parallel and with a line connecting their centers at substantially 57 with respect to their axes, thus reducing to substantially zero the magnetic couplingbetween adjacent coils. Coupling between non-adjacent coils is minimized by their special separation. The coils IIB are clamped to the insulating mounting plates I|6 by bolts |23, the ends of which engage porcelain washers |25. The cos I6 are connected in series to form the series inductive path of the artificial line while the junction points between adjacent coils are connected to the terminal plate |06 by one or more shunt capacitors CI I8 and CI I9. Various junction points in the artificial line are connected by suitable wires (not shown) to soldering lugs mounted on an insulating terminal strip |22 over a side opening |24 formed in the wall of the container |00. A suitable cover (not shown) closes the top of the box |00 and holds the coils in place.

Adjacent coils I I6 are wound in opposite directions thus securing advantageous cancellation of currents induced by external magnetic fields.

To avoid distortion, the inductances LI to L25 are of the air core type, and thus, due to their open magnetic circuits, have a pronounced tendency to pick up stray magnetic elds such as are produced by power lines and other electro-magnetic components of the instrument. The fact that adjacent coils I|6 are wound in opposite directions results in cancellation of such effects. This lack of mutual induction in the coils is furthered by their arrangement in the box |00 whereby they have parallel axes but are axially displaced sufficiently to secure a minimum of ux linkage between them. A terminating impedance coil |26, providing the inductance L25, may like- Wise be located within the box, being suitably connected between the last coil I6 of the series inductances and the terminal strip |06. The beginning and end portions of the artificial line are schematically shown in Fig. 8. The line may haveseries inductances LI to L24 and parallel capacitors CI I8 and CI I9 so as to provide twentyfour sections, plus an M-derived termination comprising inductance L25, capacitors C| and CI3I, and resistor Rl32. The circuit and constants of the artificial line are more fully disclosed in the prior Patent No. 2,382,413 and also in Patent 2,509,923, granted May 30, 1950, on the copending application of John M. Hanert, Serial No. 653,195, filed March 8, 1946, now Patent No. 2,509,923, May 30, 1950.

While we have shown and described a particular embodiment of own invention, it will be apparent to those skilled in the art that numerous modifications and variations may be made in the form and construction thereof, without departing from the more fundamental principles of the invention. We therefore desire, by the following claims, to include within the scope of our invention all such similar and modified forms of the apparatus disclosed, by which substantially the results of the invention may be obtained by supstantially the same or equivalent means.

We claim:

l. A vibrato scanning apparatus comprising a shielding casing, a circular row of stator plates secured to said casing but insulated therefrom, a shaft concentric with the circular row of stator plates, gearing including a frictional and resilient driving connection on said shaft, a shielding housing surrounding the gearing and the major portion of the shaft, a bracket secured to the shaft, a rotor plate secured to said bracket and successively cooperable with said stator plates to form a capacitative coupling therewith, said rotor plate being insulated from the shaft, a metal pin secured to said bracket and electrically connected to said rotor plate, said pin being coaxial with the shaft, and a contactor resiliently held in engagement with said pin.

2. In a device of the class described, the combination of a generally cylindrical metal casing, a plurality of groups of capacitor plates secured within the casing and arranged in a circular row, means insulating the groups of plates from one another and from the casing, means extending through the casing and insulated therefrom for making electrical connections respectively with the groups of plates, a generally cylindrical bearing housing located within the casing coaxially thereof, a shaft mounted in the housing and having an outboard end extending therefrom, a counterbalanced metallic arm secured to said outboard end of the shaft and insulated therefrom, scanning plates carried by said arm for successive capacitative coupling with said groups of capacitor plates, means to rotate said shaft, a metallic pin secured to said arm in axial alignment with the shaft, and a graphite contactor resiliently held in contact with the pin.

LAURENS HAMMOND. JOHN M. HANERT.

REFEREN CES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,671,143 Campbell May 29, 1928 1,812,828 Gray June 30, 1931 1,871,345 Rigante Aug. 9, 1932 1,873,665 Rigante Aug. 23, 1932 1,913,512 Reynolds June 13, 1933 1,971,315 Lear Aug. 21, 1934 2,116,080 Parker May 3, 1938 2,248,394 Sorensen July 8, 1941 2,388,233 Whitaker Oct. 30, 1945 2,400,619 Woodward May 21, 1946 2,416,498 Ruddock Feb. 25, 1947 2,477,635 Marchand Aug. 2, 1949 

